Means for reinforcing thin walled tubes



May 13, 1969 F. SHERWOOD MEANS FOR REINFORCING THIN WALLED TUBES Filed May 4, 1967 MZmuZm/W United States Patent U.S. Cl. 138-153 8 Claims ABSTRACT OF THE DISCLOSURE Means for reinforcing thin walled tubes comprising a resilient split sleeve applied either to the inside or outside of the tube. Additional strengthening is provided by a close fitting finned tube or rod inserted to the tube. The reinforcing means are especially suited to reinforce the thin walls of bayonet heaters, made of tantalum, for heating acids.

This invention relates to means for reinforcing thin walled tubes. The invention has been developed in connection with and will hereinafter be described in relation to tubes of tantalum employed in chemical plants and particularly as the outer casing of so-called bayonet heaters used to heat acids. Tantalum is used for this purpose since it is virtually inert to all acids except hydrofluoric acid at temperatures up to 250 C. Hitherto bayonet heaters for the above mentioned purpose have comprised one or more tantalum tubes through which steam is passed down a plain central pipe and returns inside the tube which is inserted into the acids to be heated. For reasons of efiicient heat transfer as well as for reasons of economy, tantalum being very expensive, the tubes have been made as thin as possible bearing in mind the pressure they have to withstand. The equipment has hence been very vulnerable to physical damage particularly since tantalum is a weak metal.

Although the invention has primarily been developed to reduce the vulnerability to damage of this equipment it is to be understood that the invention is not limited for this sole purpose and indeed may equally be applied to any tubes it is desired to reinforce.

According to this invention a thin walled tube is reinforced by applying thereto a substantially co-extensive resilient split sleeve.

For most applications of the invention the sleeve will be sprung inside the tube, but it may be sprung onto the outside of the tube.

According to a further feature of the invention the tube is further strengthened by inserting therein a close fitting finned tube or rod, conveniently formed of carbon steel. When the invention is applied to a thin walled tube forming the outer casing of a heat exchange unit the resilient split sleeve, which is conveniently formed of stainless steel, is preferably provided with perforations. This is to retain a direct contact between the wall of the tube and the heating or cooling medium contained therein. It has been found that this also improves heat transfer since the perforations produce turbulence in the flow of the medium within the tube.

The fins on the tube or rod inserted within the tube it is desired to strengthen are preferably arranged to extend longitudinally thereof. They may however be helically arranged if desired and further they could even be arranged circumferentially and provided with apertures or perforations for the passage of the medium passed through the tube.

One embodiment of the invention is illustrated in the accompanying drawing in which a thin walled tube 1 for 3,443,600 Patented May 13, 1969 example of tantalum is shown, within which a resilient sleeve 2 having a split 2:: is inserted, a closely fitting finned tube 3 being inserted within the split sleeve. A device of this construction is employed as a bayonet heater for heating acids. For this purpose the tube 1, which is made of any convenient length, is closed at one end so that a heating medium, for example steam, may be introduced through the tube 3 to return along the passages defined by the fins 4 between the outer surface of the tube 3 and the inner surface of the tube 1.

As already indicated the invention is not limited to a device of this nature. For example the device may not be in the form of a bayonet but of a simple tube down which a heating medium is passed in one direction only. In this case of course the finned tube 3 may be replaced by a finned rod. It is further to be understood that devices of these constructions may be employed for the purposes of cooling in addition to heating.

It has been found that heat transfer is improved if the sleeve 2 is provided with perforations or apertures as indicated at 5. Apart from enabling direct contact to take place between the inner wall of the tube 1 and the heating or cooling medium passed therethrough, the apertures also create turbulence within the tube which further improves heat transfer. In addition it has been found that transfer is augmented by conduction through the fins 4.

For certain applications perforations or apertures in the sleeve may be omitted. Further when they are provided they may be of any desired shape. When the tube has to withstand high external pressures, however, perforations, if provided are preferably in the form of a series of narrow slots, and preferably also wherever provided they are so dimensioned and arranged that the passages defined by the fins are interconnected via the perforations. This then enables any medium supplied to the tube readily to be drained away if desired. The split in the sleeve is also of assistance for this purpose, and when a bayonet heater is constructed in accordance with the present invention it is preferably horizontally arranged with the split in the sleeve arranged to be lowermost. The split in the sleeve in addition of course enables it to accommodate differences in thermal expansion or contraction between it and the tube 1.

While the invention has primarily been described in conjunction with a heating unit comprising a tube of tantalum it is to be understood, as indicated at the outset, that the invention is applicable to the reinforcement of tubes of any nature, though of course it is most beneficial when the tubes are forming the outer casing of a heat transfer unit, and the problem which the invention is desired to solve only primarily arises through the need to make such casings relatively thin. Another application of the invention would be for example the reinforcement of a thin walled thermometer pocket comprising a tube to be introduced into a liquid or gas, the temperature of which it was desired to measure.

Finally, it is to be understood that the provision of a close fitting finned tube or rod is not an essential fea ture of the invention. A resilient split sleeve alone may provide all the reinforcement required, and may as mentioned in the introduction be arranged outside rather than inside a tube. It would for example be provided outside a tube carrying a corrosive medium under pressure. The invention is also applicable to tubes or any cross-section.

What we claim is:

1. A tubular assembly comprising a thin walled tube having inner and outer surfaces, and a substantially coextensive resilient split reinforcing sleeve sprung into contact with one of said surfaces, said sleeve having only a single split. I

2. A tubular assembly according to claim 1 1n which 3 said sleeve is sprung into contact with the inner surface of said thin walled tube.

3. A tubular assembly according to claim 1 in which said sleeve is sprung into contact with the outer surface of said thin walled tube.

4. A tubular assembly according to claim 1 in which said split sleeve is provided, in addition to said single split, with perforations.

5. A tubular assembly according to claim 1 including a finned tube or rod closely fitting inside of said assembly and further reinforcing said thin walled tube.

6. A tubular assembly according to claim 1 in which said thin walled tube is of tantalum and said reinforcing sleeve is of a different metal.

, reinforcing sleeve. 0

References Cited UNITED STATES PATENTS 987,347 3/1911 Daniels et al. 29-434 2,283,424 5/1942 Colwell et a1 l38147 2,635,021 4/1953 Alward 138-440 X LOUIS K. RIMRODT, Prz'nmry Examiner. 

